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<!DOCTYPE html><html lang=en><head>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS Ruby Layout Module Level 1</title>
<link href=../default.css rel=stylesheet type=text/css>
<link href=../csslogo.ico rel="shortcut icon" type=image/x-icon>
<style>
body {
background: url("https://www.w3.org/StyleSheets/TR/logo-ED") top left no-repeat white;
background-attachment: fixed;
color: black;
font-family: sans-serif;
margin: 0 auto;
max-width: 50em;
padding: 2em 1em 2em 70px;
}
:link { color: #00C; background: transparent }
:visited { color: #609; background: transparent }
a[href]:active { color: #C00; background: transparent }
a[href]:hover { background: #ffa }
a[href] img { border-style: none }
h1, h2, h3, h4, h5, h6 { text-align: left }
h1, h2, h3 { color: #005A9C; }
h1 { font: 170% sans-serif }
h2 { font: 140% sans-serif }
h3 { font: 120% sans-serif }
h4 { font: bold 100% sans-serif }
h5 { font: italic 100% sans-serif }
h6 { font: small-caps 100% sans-serif }
.hide { display: none }
div.head { margin-bottom: 1em }
div.head h1 { margin-top: 2em; clear: both }
div.head table { margin-left: 2em; margin-top: 2em }
p.copyright { font-size: small }
p.copyright small { font-size: small }
pre { margin-left: 2em }
dt { font-weight: bold }
ul.toc, ol.toc {
list-style: none;
}
</style>
</head>
<body class=h-entry>
<div class=head>
<p data-fill-with=logo><a class=logo href=http://www.w3.org/>
<img alt=W3C height=48 src=https://www.w3.org/Icons/w3c_home width=72>
</a>
</p>
<h1 class="p-name no-ref" id=title>CSS Ruby Layout Module Level 1</h1>
<h2 class="no-num no-toc no-ref heading settled heading" id=subtitle><span class=content>Editor’s Draft,
<span class=dt-updated><span class=value-title title=20140629>29 June 2014</span></span></span></h2>
<div data-fill-with=spec-metadata><dl>
<dt>This version:
<dd><a class=u-url href=http://dev.w3.org/csswg/css-ruby-1/>http://dev.w3.org/csswg/css-ruby-1/</a>
<dt>Latest version:
<dd><a href=http://www.w3.org/TR/css-ruby-1/>http://www.w3.org/TR/css-ruby-1/</a>
<dt>Previous Versions:
<dd><dd><a href=http://www.w3.org/TR/2013/WD-css3-ruby-20130919/ rel=previous>http://www.w3.org/TR/2013/WD-css3-ruby-20130919/</a>
<dt>Feedback:
<dd><a href="mailto:www-style@w3.org?subject=%5Bcss-ruby%5D%20feedback">www-style@w3.org</a>
with subject line
“<kbd>[css-ruby] <var>… message topic …</var></kbd>”(<a href=http://lists.w3.org/Archives/Public/www-style/ rel=discussion>archives</a>)
<dt>Editors:
<dd><dd class="p-author h-card vcard"><a class="p-name fn u-url url" href=http://fantasai.inkedblade.net/contact>Elika J. Etemad</a> (<span class="p-org org">Invited Expert</span>)
<dd><dd class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:kojiishi@gluesoft.co.jp>Koji Ishii</a> (<span class="p-org org">Invited Expert</span>)
</dl>
</div>
<div data-fill-with=warning></div>
<p class=copyright data-fill-with=copyright><a href=http://www.w3.org/Consortium/Legal/ipr-notice#Copyright>Copyright</a> © 2014 <a href=http://www.w3.org/><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href=http://www.csail.mit.edu/><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href=http://www.ercim.eu/><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href=http://www.keio.ac.jp/>Keio</a>, <a href=http://ev.buaa.edu.cn/>Beihang</a>), All Rights Reserved. W3C <a href=http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer>liability</a>, <a href=http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks>trademark</a> and <a href=http://www.w3.org/Consortium/Legal/copyright-documents>document use</a> rules apply.
</p>
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc no-ref heading settled heading" id=abstract><span class=content>Abstract</span></h2>
<div class=p-summary data-fill-with=abstract><p>“Ruby” are short runs of text alongside the base text,
typically used in East Asian documents to indicate pronunciation or to provide a short annotation.
This module describes the rendering model and formatting controls related to displaying ruby annotations in CSS.</p>
<a href=http://www.w3.org/TR/CSS/>CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, in speech, etc.</div>
<h2 class="no-num no-toc no-ref heading settled heading" id=status><span class=content>Status of this document</span></h2>
<div data-fill-with=status><p>
This is a public copy of the editors’ draft.
It is provided for discussion only and may change at any moment.
Its publication here does not imply endorsement of its contents by W3C.
Don’t cite this document other than as work in progress.
<p>
The (<a href=http://lists.w3.org/Archives/Public/www-style/>archived</a>) public mailing list
<a href="mailto:www-style@w3.org?Subject=%5Bcss-ruby%5D%20PUT%20SUBJECT%20HERE">www-style@w3.org</a>
(see <a href=http://www.w3.org/Mail/Request>instructions</a>)
is preferred for discussion of this specification.
When sending e-mail,
please put the text “css-ruby” in the subject,
preferably like this:
“[css-ruby] <em>…summary of comment…</em>”
<p>
This document was produced by the <a href=http://www.w3.org/Style/CSS/members>CSS Working Group</a>
(part of the <a href=http://www.w3.org/Style/>Style Activity</a>).
<p>
This document was produced by a group operating under
the <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/>5 February 2004 W3C Patent Policy</a>.
W3C maintains a <a href=http://www.w3.org/2004/01/pp-impl/32061/status rel=disclosure>public list of any patent disclosures</a>
made in connection with the deliverables of the group;
that page also includes instructions for disclosing a patent.
An individual who has actual knowledge of a patent which the individual believes contains <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential>Essential Claim(s)</a>
must disclose the information in accordance with <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure>section 6 of the W3C Patent Policy</a>.</div>
<div data-fill-with=at-risk></div>
<h2 class="no-num no-toc no-ref heading settled heading" id=contents><span class=content>Table of Contents</span></h2>
<div data-fill-with=table-of-contents><ul class=toc>
<li><a href=#intro><span class=secno>1</span> Introduction</a>
<ul class=toc>
<li><a href=#placement><span class=secno>1.1</span> Module interactions</a>
<li><a href=#values><span class=secno>1.2</span> Values</a>
<li><a href=#diagram-conventions><span class=secno>1.3</span> Diagram conventions</a>
<li><a href=#ruby-def><span class=secno>1.4</span> What is ruby?</a></ul>
<li><a href=#ruby-model><span class=secno>2</span> Ruby Formatting Model</a>
<ul class=toc>
<li><a href=#ruby-display><span class=secno>2.1</span> Ruby-specific <span>display</span> property values</a>
<li><a href=#box-fixup><span class=secno>2.2</span> Anonymous Ruby Box Generation</a>
<ul class=toc>
<li><a href=#block-ruby><span class=secno>2.2.1</span> Block-level Ruby</a></ul>
<li><a href=#pairing><span class=secno>2.3</span> Ruby Pairing and Annotation Levels</a>
<ul class=toc>
<li><a href=#nested-pairing><span class=secno>2.3.1</span> Nested Ruby</a></ul>
<li><a href=#autohide><span class=secno>2.4</span> Autohiding Annotations</a>
<li><a href=#white-space><span class=secno>2.5</span> White Space</a>
<li><a href=#ruby-layout><span class=secno>2.6</span> Ruby layout</a>
<ul class=toc>
<li><a href=#inter-character-layout><span class=secno>2.6.1</span> Inter-character ruby layout</a></ul>
<li><a href=#box-style><span class=secno>2.7</span> Styling Ruby Boxes</a>
<li><a href=#line-breaks><span class=secno>2.8</span> Ruby box and line breaking</a>
<ul class=toc>
<li><a href=#break-between><span class=secno>2.8.1</span> Breaking between bases</a>
<li><a href=#break-within><span class=secno>2.8.2</span> Breaking within bases</a></ul>
<li><a href=#ruby-bidi><span class=secno>2.9</span> Bidi Reordering</a>
<li><a href=#line-height><span class=secno>2.10</span> Ruby box and line stacking</a></ul>
<li><a href=#ruby-props><span class=secno>3</span> Ruby Properties</a>
<ul class=toc>
<li><a href=#rubypos><span class=secno>3.1</span> Ruby positioning: the <span>ruby-position</span> property</a>
<li><a href=#collapsed-ruby><span class=secno>3.2</span> Collapsed Ruby Annotations: the <span>ruby-merge</span> property</a>
<li><a href=#ruby-align-property><span class=secno>3.3</span> <span></span> Ruby Text Distribution: the <span>ruby-align</span> property</a></ul>
<li><a href=#edge-effects><span class=secno>4</span> Edge Effects</a>
<ul class=toc>
<li><a href=#ruby-overhang><span class=secno>4.1</span> Overhanging Ruby</a>
<li><a href=#line-edge><span class=secno>4.2</span> Line-edge Alignment</a></ul>
<li><a href=#default-stylesheet><span class=secno></span> Appendix A: Default Style Sheet</a>
<ul class=toc>
<li><a href=#default-ua-ruby><span class=secno></span> <span class=secno>A.1</span> Supporting Ruby Layout</a>
<li><a href=#default-inline><span class=secno></span> <span class=secno>A.2</span> Inlining Ruby Annotations</a>
<li><a href=#default-parens><span class=secno></span> <span class=secno>A.3</span> Generating Parentheses</a></ul>
<li><a href=#glossary><span class=secno>5</span> Glossary</a>
<li><a href=#acknowledgments><span class=secno></span> Acknowledgments</a>
<li><a href=#changes><span class=secno></span> Changes</a>
<li><a href=#conformance><span class=secno></span> Conformance</a>
<ul class=toc>
<li><a href=#conventions><span class=secno></span> Document conventions</a>
<li><a href=#conformance-classes><span class=secno></span> Conformance classes</a>
<li><a href=#partial><span class=secno></span> Partial implementations</a>
<li><a href=#experimental><span class=secno></span> Experimental implementations</a>
<li><a href=#testing><span class=secno></span> Non-experimental implementations</a></ul>
<li><a href=#references><span class=secno></span> References</a>
<ul class=toc>
<li><a href=#normative><span class=secno></span> Normative References</a>
<li><a href=#informative><span class=secno></span> Informative References</a></ul>
<li><a href=#index><span class=secno></span> Index</a>
<li><a href=#property-index><span class=secno></span> Property index</a>
<li><a href=#issues-index><span class=secno></span> Issues Index</a></ul></div>
<p></p>
<h2 class="heading settled heading" data-level=1 id=intro><span class=secno>1 </span><span class=content>
Introduction</span><a class=self-link href=#intro></a></h2>
<p><em>This section is not normative.</em>
<h3 class="heading settled heading" data-level=1.1 id=placement><span class=secno>1.1 </span><span class=content>
Module interactions</span><a class=self-link href=#placement></a></h3>
<p>This module extends the inline box model of CSS Level 2 <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=biblio-css21>[CSS21]</a>
to support ruby.
<p>None of the properties in this module apply to the <code>::first-line</code> or
<code>::first-letter</code> pseudo-elements.
<h3 class="heading settled heading" data-level=1.2 id=values><span class=secno>1.2 </span><span class=content>
Values</span><a class=self-link href=#values></a></h3>
<p>This specification follows the
<a href=http://www.w3.org/TR/CSS21/about.html#property-defs>CSS property
definition conventions</a> from <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=biblio-css21>[CSS21]</a>. Value types not defined in
this specification are defined in CSS Level 2 Revision 1 <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=biblio-css21>[CSS21]</a>.
Other CSS modules may expand the definitions of these value types: for
example <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3val title=biblio-css3val>[CSS3VAL]</a>, when combined with this module, expands the
definition of the <var><length></var> value type as used in this specification.</p>
<p>In addition to the property-specific values listed in their definitions,
all properties defined in this specification also accept the
<a href=http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit>inherit</a>
keyword as their property value. For readability it has not been repeated
explicitly.
<h3 class="heading settled heading" data-level=1.3 id=diagram-conventions><span class=secno>1.3 </span><span class=content>
Diagram conventions</span><a class=self-link href=#diagram-conventions></a></h3>
<p>Many typographical conventions in East Asian typography depend
on whether the character rendered is wide (CJK) or narrow (non-CJK).
There are a number of illustrations in this document
for which the following legend is used:
<dl>
<dt><img alt="Symbolic wide-cell glyph representation" height=39 src=images/fullwidth.gif width=39>
<dd>Wide-cell glyph (e.g. Han) that is the <var>n</var>th character in the text run.
They are typically sized to 50% when used as annotations.
<dt><img alt="Symbolic narrow-cell glyph representation" height=39 src=images/halfwidth.gif width=19>
<dd>Narrow-cell glyph (e.g. Roman) which is the <var>n</var>th glyph in the text run.
</dl>
<p>The orientation which the above symbols assume in the diagrams
corresponds to the orientation that the glyphs they represent
are intended to assume when rendered by the user agent.
Spacing between these characters in the diagrams is incidental,
unless intentionally changed to make a point.
<h3 class="heading settled heading" data-level=1.4 id=ruby-def><span class=secno>1.4 </span><span class=content>
What is ruby?</span><a class=self-link href=#ruby-def></a></h3>
<p><dfn data-dfn-type=dfn data-noexport="" id=ruby>Ruby<a class=self-link href=#ruby></a></dfn> is the commonly-used name for a run of text
that appears alongside another run of text (referred to as the “base”)
and serves as an annotation or a pronunciation guide associated with that run of text.
<p>The following figures show two examples of Ruby,
a simple case and one with more complicated structure.
<div class=example>
<p>In this first example, a single annotation is used to annotate the base text.
<div class=figure>
<p><img alt="Example of ruby applied on top of a Japanese expression" src=images/licence.png>
<p class=caption>Example of ruby used in Japanese (simple case)
</div>
<p>In Japanese typography, this case is sometimes called
<span lang=ja>taigo</span> ruby or group-ruby (per-word ruby),
because the annotation as a whole is associated
with multi-character word (as a whole).
</div>
<div class=example>
<p>In this second example,
two levels of annotations are attached to a base sequence:
the hiragana characters on top refer to the pronunciation of each of the base kanji characters,
while the words “Keio” and “University” on the bottom are annotations describing the English translation.
<div class=figure>
<p><img alt="Example showing complex ruby with annotation text over and under the base characters" src=images/ruby-univ.gif>
<p class=caption>Complex ruby with annotation text over and under the base characters
</div>
<p>
<p>Notice that to allow correct association between the hiragana characters and
their corresponding Kanji base characters,
the spacing between these Kanji characters is adjusted.
(This happens around the fourth Kanji character in the figure above.)
To avoid variable spacing between the Kanji characters in the example above
the hiragana annotations can be styled as a <a data-link-type=dfn href=#collapsed-annotation title="collapsed annotation">collapsed annotation</a>,
which will look more like the group-ruby example earlier.
However because the base-annotation pairings are recorded in the ruby structure,
if the text breaks across lines, the annotation characters will stay
correctly paired with their respective base characters.
</div>
<p><a data-link-type=dfn href=#ruby title=ruby>Ruby</a> formatting as used in Japanese is described in JIS X-4051 <a data-biblio-type=informative data-link-type=biblio href=#biblio-jis4051 title=biblio-jis4051>[JIS4051]</a> (in Japanese)
and in Requirements for Japanese Text Layout <a data-biblio-type=informative data-link-type=biblio href=#biblio-jlreq title=biblio-jlreq>[JLREQ]</a> (in English and Japanese)].
In HTML, ruby structure and markup to represent it is described
in the Ruby Markup Extension specification.
This module describes the CSS rendering model
and formatting controls relevant to ruby layout of such markup.
<h2 class="heading settled heading" data-level=2 id=ruby-model><span class=secno>2 </span><span class=content>
Ruby Formatting Model</span><a class=self-link href=#ruby-model></a></h2>
<p>The CSS ruby model is based on
the <a href=http://darobin.github.io/html-ruby/>HTML Ruby Markup Extension</a>
and <a href=http://www.w3.org/TR/ruby/>XHTML Ruby Annotation Recommendation</a> <a data-biblio-type=informative data-link-type=biblio href=#biblio-ruby title=biblio-ruby>[RUBY]</a>.
In this model, a ruby structure consists of
one or more <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> elements representing the base (annotated) text,
associated with one or more levels of <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a> elements representing the annotations.
The structure of ruby is similar to that of a table:
there are “rows” (the <a data-link-type=dfn href=#base-level title="base level">base text level</a>, each <a data-link-type=dfn href=#annotation-level title="annotation level">annotation level</a>)
and “columns” (each <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> and its corresponding <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a>).
<p>Consecutive bases and annotations are grouped together into <dfn data-dfn-type=dfn data-noexport="" id=ruby-segments>ruby segments<a class=self-link href=#ruby-segments></a></dfn>.
Within a <a data-link-type=dfn href=#ruby-segments title="ruby segment">ruby segment</a>, a <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a> may span multiple <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>.
<p class=note>In HTML, a single <code><ruby></code> element may contain multiple <a data-link-type=dfn href=#ruby-segments title="ruby segments">ruby segments</a>.
(In the XHTML Ruby model, a single <code><ruby></code> element can only contain one <a data-link-type=dfn href=#ruby-segments title="ruby segment">ruby segment</a>.)
<h3 class="heading settled heading" data-level=2.1 id=ruby-display><span class=secno>2.1 </span><span class=content>
Ruby-specific <a class=property data-link-type=propdesc href=#propdef-display title=display>display</a> property values</span><a class=self-link href=#ruby-display></a></h3>
<p>For document languages (such as XML applications) that do not have pre-defined ruby elements,
authors must map document language elements to ruby elements;
this is done with the <a class=property data-link-type=propdesc href=#propdef-display title=display>display</a> property.
<table class=propdef>
<tr>
<th>Name:
<td><dfn class=css-code data-dfn-type=property data-export="" id=propdef-display>display<a class=self-link href=#propdef-display></a></dfn><tr>
<th><a href=#values>New Values</a>:
<td>ruby | ruby-base | ruby-text | ruby-base-container | ruby-text-container
</table>
<p>The following new <a class=property data-link-type=propdesc href=#propdef-display title=display>display</a> values assign ruby layout roles to an arbitrary element:
<dl data-dfn-for=display>
<dt><a class=css data-link-type=maybe href=#ruby title=ruby>ruby</a>
<dd>Specifies that an element generates a <dfn data-dfn-type=dfn data-noexport="" id=ruby-container title="ruby container | ruby container box">ruby container box<a class=self-link href=#ruby-container></a></dfn>.
(Corresponds to HTML/XHTML <code><ruby></code> elements.)
<dt><span class=css data-link-type=maybe title=ruby-base>ruby-base</span>
<dd>Specifies that an element generates a <dfn data-dfn-type=dfn data-noexport="" id=ruby-base-box title="ruby base box | ruby base">ruby base box<a class=self-link href=#ruby-base-box></a></dfn>.
(Corresponds to HTML/XHTML <code><rb></code> elements.)
<dt><span class=css data-link-type=maybe title=ruby-text>ruby-text</span>
<dd>Specifies that an element generates a <dfn data-dfn-type=dfn data-noexport="" id=ruby-annotation-box title="ruby annotation box | ruby annotation | annotation">ruby annotation box<a class=self-link href=#ruby-annotation-box></a></dfn>.
(Corresponds to HTML/XHTML <code><rt></code> elements.)
<dt><span class=css data-link-type=maybe title=ruby-base-container>ruby-base-container</span>
<dd>Specifies that an element generates a <dfn data-dfn-type=dfn data-noexport="" id=ruby-base-container-box title="ruby base container box | ruby base container">ruby base container box<a class=self-link href=#ruby-base-container-box></a></dfn>.
(Corresponds to XHTML <code><rbc></code> elements; generated as an anonymous box in HTML.)
<dt><span class=css data-link-type=maybe title=ruby-text-container>ruby-text-container</span>
<dd>Specifies that an element generates a <dfn data-dfn-type=dfn data-noexport="" id=ruby-annotation-container-box title="ruby annotation container box | ruby annotation container">ruby annotation container box<a class=self-link href=#ruby-annotation-container-box></a></dfn>.
(Corresponds to HTML/XHTML <code><rtc></code> elements.)
</dl>
<h3 class="heading settled heading" data-level=2.2 id=box-fixup><span class=secno>2.2 </span><span class=content>
Anonymous Ruby Box Generation</span><a class=self-link href=#box-fixup></a></h3>
<p>The CSS model does not require that the document language
include elements that correspond to each of these components.
Missing parts of the structure are implied through the anonymous box generation rules
<a href=http://www.w3.org/TR/CSS21/tables.html#anonymous-boxes>similar to those used to normalize tables</a>. <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=biblio-css21>[CSS21]</a>
<dl>
<style scoped>
dt { counter-increment: box-fixup; }
dt::before { content: counter(box-fixup) ". "; }
</style>
<dt id=anon-gen-inlinize><a class=self-link href=#anon-gen-inlinize></a>Inlinize Block-level Boxes
<dd>
Any in-flow block-level boxes directly contained by a
<a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>,
<a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>,
<a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>,
<a data-link-type=dfn href=#ruby-base-box title="ruby base box">ruby base box</a>,
or <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation box">ruby annotation box</a>
are forced to be inline-level boxes,
and their <a class=property data-link-type=propdesc href=#propdef-display title=display>display</a> value computed accordingly.
For example,
the <a class=property data-link-type=propdesc href=#propdef-display title=display>display</a> property of an in-flow element with <a class=css data-link-type=propdesc href=#propdef-display title=display>display: block</a>
parented by an element with <a class=css data-link-type=propdesc href=#propdef-display title=display>display: ruby-text</a>
computes to <span class=css data-link-type=maybe title=inline-block>inline-block</span>.
This computation occurs after any intermediary anonymous-box fixup
(such as that required by internal table elements).
<dt id=anony-gen-trim-space><a class=self-link href=#anony-gen-trim-space></a>Trim leading/trailing white space
<dd>
Any white space within a ruby structure is discarded
at the beginning and end of
a <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>, <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>, or <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>.
<dt id=anon-gen-bare-inlines><a class=self-link href=#anon-gen-bare-inlines></a>Wrap misparented inline-level content
<dd>
Any consecutive sequence of text and inline-level boxes
directly parented by a <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a> or <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>
is wrapped in an anonymous <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a>.
Similarly, any consecutive sequence of text and inline-level boxes
directly parented by a <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>
is wrapped in an anonymous <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a>.
<dt id=anon-gen-discard-space><a class=self-link href=#anon-gen-discard-space></a>Remove inter-level white space
<dd>
Any anonymous <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> containing only white space that
both immediately follows a box of type A
and is immediately followed by at box of its corresponding type B
as defined in the table below
is removed, as if it had <a class=css data-link-type=propdesc href=#propdef-display title=display>display: none</a>.
<table class=data>
<thead>
<tr><th>A
<th>B
<tbody>
<tr><td><a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> or <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>
<td><a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a> or <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>
<tr><td><a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>
<td><a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>
<tr><td><a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a>
<td><a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>
<tr><td><a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>
<td><a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a>
</table>
<dt id=anon-gen-interpret-space><a class=self-link href=#anon-gen-interpret-space></a>Interpret intra-level white space
<dd>
<ul>
<li>Any anonymous <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> containing only white space that
both immediately follows a <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a> or <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>
and is immediately followed by a <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> or <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>
is labelled as <dfn data-dfn-type=dfn data-noexport="" id=inter-segment-white-space>inter-segment white space<a class=self-link href=#inter-segment-white-space></a></dfn>
(and treated specially for pairing and layout, see below).
<li>Any anonymous <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> containing only white space that is
both immediately follows and is immediately followed by a <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a>
is labelled as <dfn data-dfn-type=dfn data-noexport="" id=inter-base-white-space>inter-base white space<a class=self-link href=#inter-base-white-space></a></dfn>
(and treated specially for pairing and layout, see below).
<li>Any anonymous <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a> containing only white space that is
both immediately follows and is immediately followed by a <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a>
is labelled as <dfn data-dfn-type=dfn data-noexport="" id=inter-annotation-white-space>inter-annotation white space<a class=self-link href=#inter-annotation-white-space></a></dfn>
(and treated specially for pairing and layout, see below).
</ul>
<dt id=anon-gen-anon-containers><a class=self-link href=#anon-gen-anon-containers></a>Generate anonymous level containers
<dd>
Any consecutive sequence of <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a> and <a data-link-type=dfn href=#inter-base-white-space title="inter-base white space">inter-base white space</a>
(and not <a data-link-type=dfn href=#inter-segment-white-space title="inter-segment white space">inter-segment white space</a>)
not parented by a <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>
is wrapped in an anonymous <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>.
Similarly, any consecutive sequence of <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a> and <a data-link-type=dfn href=#inter-annotation-white-space title="inter-annotation white space">inter-annotation white space</a>
not parented by a <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>
is wrapped in an anonymous <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>.
<dt id=anon-gen-anon-ruby><a class=self-link href=#anon-gen-anon-ruby></a>Generate anonymous ruby containers
<dd>
A sequence of <a data-link-type=dfn href=#ruby-base-container-box title="ruby base containers">ruby base containers</a>, <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation containers">ruby annotation containers</a>, and/or <a data-link-type=dfn href=#inter-segment-white-space title="inter-segment white space">inter-segment white space</a>
not parented by a <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>
is wrapped in an anonymous <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>.
<dt id=anon-gen-unbreak><a class=self-link href=#anon-gen-unbreak></a>Suppress line breaks
<dd>
Convert all forced line breaks inside <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a> (regardless of <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-text-3/#propdef-white-space title=white-space>white-space</a> value)
as defined for <i data-link-type=dfn title=collapsible>collapsible</i> segment breaks in <a href=http://www.w3.org/TR/css-text-3/#line-break-transform>CSS Text Level 3 § 4.1.2</a>.
<p class=issue id=issue-8af70305><a class=self-link href=#issue-8af70305></a>The goal of this is to simplify the layout model by suppressing any line breaks within ruby annotations.
Alternatively we could try to define some kind of acceptable behavior for them.
</dl>
<p class=issue id=issue-f2086090><a class=self-link href=#issue-f2086090></a>Make this into an example:
<img src=http://lists.w3.org/Archives/Public/www-archive/2014Jun/att-0027/PastedGraphic-1.png style="display: block; width: 100%">
<p>At this point, all ruby layout structures are properly parented,
and the UA can start to associate bases with their annotations.
<p class=note>
Note that the UA is not required to create any of these anonymous boxes in its internal structures,
as long as pairing and layout behaves as if they existed.
<h4 class="heading settled heading" data-level=2.2.1 id=block-ruby><span class=secno>2.2.1 </span><span class=content>
Block-level Ruby</span><a class=self-link href=#block-ruby></a></h4>
<p>If an element has a computed <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-display-3/#propdef-display-inside title=display-inside>display-inside</a> of <a class=css data-link-type=maybe href=#ruby title=ruby>ruby</a>
and a computed <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-display-3/#propdef-display-outside title=display-outside>display-outside</a> other than <span class=css data-link-type=maybe title=inline-level>inline-level</span>,
then it generates two boxes:
a principal block container box of the required <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-display-3/#propdef-display-outside title=display-outside>display-outside</a> type,
and an inline-level <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>.
All properties specified on the element apply to the principal box
(and if inheritable, inherit to the <a data-link-type=dfn href=#ruby-container title="ruby container box">ruby container box</a>).
This allows styling the element as a block,
while correctly maintaining the internal ruby structure.
<p>See the <a href=http://www.w3.org/TR/css-display/>CSS Display Module</a>
for more information on <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-display-3/#propdef-display-inside title=display-inside>display-inside</a> and <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-display-3/#propdef-display-outside title=display-outside>display-outside</a>.
<h3 class="heading settled heading" data-level=2.3 id=pairing><span class=secno>2.3 </span><span class=content>
Ruby Pairing and Annotation Levels</span><a class=self-link href=#pairing></a></h3>
<p>Within a ruby structure,
each <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> is associated with <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a>
and vice versa.
A <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> can be associated with at most one <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a> per <a data-link-type=dfn href=#annotation-level title="annotation level">annotation level</a>.
If there are multiple <a data-link-type=dfn href=#annotation-level title="annotation levels">annotation levels</a>, it can therefore be associated with multiple <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a>.
A <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a> is associated with one or more <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>;
annotations can span multiple bases.
<p><dfn data-dfn-type=dfn data-noexport="" id=annotation-pairing>Annotation pairing<a class=self-link href=#annotation-pairing></a></dfn> is the process of associating
<a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a> with <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>.
<ol>
<li>
<p>First, the ruby structure is divided into <a data-link-type=dfn href=#ruby-segments title="ruby segments">ruby segments</a>,
each consisting of a single <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>
followed by one or more <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation containers">ruby annotation containers</a>.
If the first child of a <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a> is a <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>,
an anonymous, empty <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a> is assumed to exist before it.
Similarly, if the <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a> contains consecutive <a data-link-type=dfn href=#ruby-base-container-box title="ruby base containers">ruby base containers</a>,
anonymous, empty <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation containers">ruby annotation containers</a> are assumed to exist between them.
The <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a> in each segment is thus associated
with each of the <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation containers">ruby annotation containers</a> in that segment.
<p>Each <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a> in a <a data-link-type=dfn href=#ruby-segments title="ruby segment">ruby segment</a>
represents one <dfn data-dfn-type=dfn data-noexport="" id=annotation-level title="annotation level | level">level<a class=self-link href=#annotation-level></a></dfn> of annotation:
the first one represents the first level of annotation,
the second one represents the second level of annotation,
and so on.
The <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a> represents the <dfn data-dfn-type=dfn data-noexport="" id=base-level>base level<a class=self-link href=#base-level></a></dfn>.
<li>Within each <a data-link-type=dfn href=#ruby-segments title="ruby segment">ruby segment</a>,
each <a data-link-type=dfn href=#ruby-base-box title="ruby base box">ruby base box</a> in the <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>
is paired with one <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation box">ruby annotation box</a>
from each <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a> in its <a data-link-type=dfn href=#ruby-segments title="ruby segment">ruby segment</a>.
If there are not enough <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a> in a <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>,
the last one is associated with any excess <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>.
(If there are not any in the <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>, an anonymous empty one is assumed to exist.)
If there are not enough <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>,
any remaining <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a> are assumed to be associated
with empty, anonymous bases inserted at the end of the <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>.
<p>If an implementation supports ruby markup with explicit spanning
(e.g. XHTML Complex Ruby Annotations),
it must adjust the pairing rules to pair spanning annotations to multiple bases
appropriately.
</ol>
<p>At this point, ruby “columns” are defined,
each represented by a single <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a>
and associated with one <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a> (possibly an empty, anonymous one)
from each <a data-link-type=dfn href=#annotation-level title="annotation level">annotation level</a>.
<h4 class="heading settled heading" data-level=2.3.1 id=nested-pairing><span class=secno>2.3.1 </span><span class=content>
Nested Ruby</span><a class=self-link href=#nested-pairing></a></h4>
<p>When <a data-link-type=dfn href=#ruby-container title="ruby containers">ruby containers</a> are nested,
pairing begins with the deepest <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>,
then expands out,
treating each <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a> nested within another <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>
essentially as a single <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> in the outer <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>,
and associating each <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a>
paired with the nested <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>
as being associated with (spanning) all of its <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>.
<p>Using nested <a data-link-type=dfn href=#ruby-container title="ruby containers">ruby containers</a> thus allows the representation
of complex spanning relationships.
<p class=issue id=issue-2f9c28f2><a class=self-link href=#issue-2f9c28f2></a>This has to be Level 1 because HTML5 allows it, so we have to handle it. Yay HTML5.
<h3 class="heading settled heading" data-level=2.4 id=autohide><span class=secno>2.4 </span><span class=content>
Autohiding Annotations</span><a class=self-link href=#autohide></a></h3>
<p>If a <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a> has the exact same text content as its base,
it is <dfn data-dfn-type=dfn data-noexport="" id=hidden-ruby-annotation title="hidden ruby annotation | hidden annotation">hidden<a class=self-link href=#hidden-ruby-annotation></a></dfn>.
Hiding a <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a> does not affect annotation pairing
or the block-axis positioning of boxes in other <a data-link-type=dfn href=#annotation-level title=levels>levels</a>.
However the <a data-link-type=dfn href=#hidden-ruby-annotation title="hidden annotation">hidden annotation</a> is not visible,
and it has no impact on layout
other than to separate adjacent sequences of <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation boxes">ruby annotation boxes</a> within its level,
as if they belonged to separate segments
and the <a data-link-type=dfn href=#hidden-ruby-annotation title="hidden annotation">hidden annotation</a>’s base were not a <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> but an intervening inline.
<div class=example>
<p>This is to allow correct inlined display of annotations
for Japanese words that are a mix of kanji and hiragana.
For example, the word <span lang=ja>振り仮名</span> should be inlined as
<p class=figure>振り仮名(ふりがな)
<p>and therefore marked up as
<pre><ruby>
<rb>振</rb><rb>り</rb><rb>仮</rb><rb>名</rb>
<rp>(</rp><rt>ふ</rt><rt>り</rt><rt>が</rt><rt>な</rt><rp>)</rp>
<ruby></pre>
<p>However, when displayed as ruby, the “り” should be hidden
<div class=figure>
<p><img alt="Hiragana annotations for 振り仮名 appear, each pronunciation above its kanji base character." src=images/furigana-separate.png>
<p class=caption>Hiragana ruby for 振り仮名. Notice there is no hiragana annotation above り, since it is already in hiragana.
</div>
</div>
<p class=note>
Future levels of CSS Ruby may add controls for this,
but in this level it is always forced.
<p>The content comparison for this auto-hiding behavior
takes place prior to white space collapsing (<a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-text-3/#propdef-white-space title=white-space>white-space</a>) and text transformation (<a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-text-3/#propdef-text-transform title=text-transform>text-transform</a>)
and ignores elements (considers only the <code>textContent</code> of the boxes).
<h3 class="heading settled heading" data-level=2.5 id=white-space><span class=secno>2.5 </span><span class=content>
White Space</span><a class=self-link href=#white-space></a></h3>
<p><i data-link-type=dfn title="collapsible white space">Collapsible white space</i> within a ruby structure is discarded
<ul>
<li>at the beginning and end of a <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>, <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>, or <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>,
<li>at the beginning/end of a <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation box">ruby annotation box</a> or <a data-link-type=dfn href=#ruby-base-box title="ruby base box">ruby base box</a> if white space is not its only contents,
<li>between a <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a> and its following <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>,
<li>between <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation containers">ruby annotation containers</a>.
</ul>
<p>Between <a data-link-type=dfn href=#ruby-segments title="ruby segments">ruby segments</a>, between <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>, and between <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a>, however,
white space is not discarded.
<p>Where undiscarded white space is <i data-link-type=dfn title=collapsible>collapsible</i>, it will collapse
following the standard <a href=http://www.w3.org/TR/css3-text/#white-space-rules>white space processing rules</a>. <a data-biblio-type=normative data-link-type=biblio href=#biblio-css3text title=biblio-css3text>[CSS3TEXT]</a>
For <i data-link-type=dfn title=collapsible>collapsible</i> white space between <a data-link-type=dfn href=#ruby-segments title="ruby segments">ruby segments</a>, however,
the contextual text for determining collapsing behavior is given by the <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a> on either side,
not the text on either side of the white space in the source document.
<div class=note>
<p>Note that the white space processing rules
cause a white space sequence containing a <i data-link-type=dfn title="segment break">segment break</i> (such as a line feed)
to <a href=http://www.w3.org/TR/css3-text/#line-break-transform>collapse to nothing</a> between CJK characters.
This means that CJK ruby can safely use white space for indentation of the ruby markup.
For example, the following markup will display without any spaces:
<pre><ruby>
<rb>東</rb><rb>京</rb>
<rt>とう</rt><rt>きょう</rt>
</ruby></pre>
<p>However, white space that does not contain a <i data-link-type=dfn title="segment break">segment break</i> does not collapse completely away,
so this markup will display with a space between the first and second ruby pairs:
<pre><ruby>
<rb>東</rb> <rb>京</rb>
<rt>とう</rt> <rt>きょう</rt>
</ruby></pre>
</div>
<p>Any preserved white space is then wrapped in an anonymous box belonging to
the <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a> (if between <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>),
<a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a> (if between <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a>),
or <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a> (if between <a data-link-type=dfn href=#ruby-segments title="ruby segments">ruby segments</a>).
In the latter case, the text is considered part of the <a data-link-type=dfn href=#base-level title="base level">base level</a>.
Such anonymous boxes do not take part in pairing.
They merely ensure separation between adjacent bases/annotations.
<p class=issue id=issue-1851041e><a class=self-link href=#issue-1851041e></a>Specify how these anonymous white space boxes impact layout.
<div class=example>
<p>These rules allow ruby to be used with space-separated scripts such as Latin.
For example,
<pre><ruby>
<rb>W</rb><rb>W</rb><rb>W</rb>
<rt>World</rt> <rt>Wide</rt> <rt>Web</rt>
</ruby></pre>
<p>They also ensure that annotated white space is preserved. For example,
<pre><ruby>
<rb>Aerith</rb><rb> </rb><rb>Gainsboro</rb>
<rt>エアリス</rt><rt>・</rt><rt>ゲインズブール</rt>
</ruby></pre>
</div>
<h3 class="heading settled heading" data-level=2.6 id=ruby-layout><span class=secno>2.6 </span><span class=content>
Ruby layout</span><a class=self-link href=#ruby-layout></a></h3>
<p>When a ruby structure is laid out,
its <a data-link-type=dfn href=#base-level title="base level">base level</a> is laid out on the line,
aligned according to its <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-vertical-align title=vertical-align>vertical-align</a> property
exactly as if its <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a> were a regular sequence of inline boxes.
Each <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a> is sized and positioned
to contain exactly the full height of its <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>.
<p><a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">Ruby annotations</a> associated with the <a data-link-type=dfn href=#base-level title="base level">base level</a>
are then positioned with respect to their <a data-link-type=dfn href=#ruby-base-box title="ruby base boxes">ruby base boxes</a>
according to the applicable <a class=property data-link-type=propdesc href=#propdef-ruby-position title=ruby-position>ruby-position</a> values.
<a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">Ruby annotations</a> within a level (within a single <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>)
are aligned to each other as if they were inline boxes
participating in the same inline formatting context.
Each <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a> is sized and positioned
to contain exactly the full height of its <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a>.
<p>A ruby container (or fragment thereof)
measures as wide as the content of its widest level.
Similarly, <a data-link-type=dfn href=#ruby-base-box title="ruby base boxes">ruby base boxes</a> and <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation boxes">ruby annotation boxes</a>
within a ruby “column” have the measure of the widest content in that “column”.
In the case of spanning <a data-link-type=dfn href=#ruby-annotation-box title=annotations>annotations</a>
(whether actually spanning or pretending to span per <a class=property data-link-type=propdesc href=#propdef-ruby-merge title=ruby-merge>ruby-merge</a>),
the measures of the <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation box">ruby annotation box</a> and
the sum of its associated <a data-link-type=dfn href=#ruby-base-box title="ruby base boxes">ruby base boxes</a> must match.
<p>How the extra space is distributed
when ruby content is narrower than the measure of its box
is specified by the <a class=property data-link-type=propdesc href=#propdef-ruby-align title=ruby-align>ruby-align</a> property.
<h4 class="heading settled heading" data-level=2.6.1 id=inter-character-layout><span class=secno>2.6.1 </span><span class=content>
Inter-character ruby layout</span><a class=self-link href=#inter-character-layout></a></h4>
<p>Inter-character annotations have special layout.
When <a class=property data-link-type=propdesc href=#propdef-ruby-position title=ruby-position>ruby-position</a> indicates <a class=css data-link-type=maybe href=#valdef-ruby-position.inter-character title=inter-character>inter-character</a> annotations,
the affected <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation boxes">ruby annotation boxes</a>
are spliced into and measured as part of the layout of the <a data-link-type=dfn href=#base-level title="base level">base level</a>.
The <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a> must be sized to include both the <a data-link-type=dfn href=#ruby-base-box title="ruby base boxes">ruby base boxes</a>
as well as the <a class=css data-link-type=maybe href=#valdef-ruby-position.inter-character title=inter-character>inter-character</a> <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation boxes">ruby annotation boxes</a>.
The affected <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a> is similarly sized
so that its content box coincides with that of the <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>.
<p>For the purpose of laying out other levels of annotations,
an <a class=css data-link-type=maybe href=#valdef-ruby-position.inter-character title=inter-character>inter-character</a> annotation effectively becomes part of its base.
<span class=issue id=issue-029133da><a class=self-link href=#issue-029133da></a>Or should it become a quasi-base between two bases?</span>
A spanning <a class=css data-link-type=maybe href=#valdef-ruby-position.inter-character title=inter-character>inter-character</a> annotation is placed after
all the bases that it spans.
<h3 class="heading settled heading" data-level=2.7 id=box-style><span class=secno>2.7 </span><span class=content>
Styling Ruby Boxes</span><a class=self-link href=#box-style></a></h3>
<p>In most respects, ruby boxes can be styled similar to inline boxes.
However, the UA is not required to support
any of the box properties (borders, margins, padding),
any of the background properties or outline properties,
or any other property that illustrates the bounds of the box
on <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container boxes">ruby base container boxes</a>, <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container boxes">ruby annotation container boxes</a>,
or <a href=#nested-pairing>ruby-internal <a data-link-type=dfn href=#ruby-container title="ruby container boxes">ruby container boxes</a></a>.
The UA may implement these boxes simply as abstractions for inheritance
and control over the layout of their contents.
<h3 class="heading settled heading" data-level=2.8 id=line-breaks><span class=secno>2.8 </span><span class=content>
Ruby box and line breaking</span><a class=self-link href=#line-breaks></a></h3>
<p>When there is not enough space for an entire <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a> to fit on the line,
the ruby may be broken wherever all levels simultaneously allow a break.
Ruby most often breaks between base-annotation sets,
but if the line-breaking rules allow it, can also break within a <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a>
(and, in parallel, its associated <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation boxes">ruby annotation boxes</a>).
<p>Whenever ruby breaks across lines, <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a> must stay
with their respective <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>.
The line <em>must not</em> break between a <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> and its <a data-link-type=dfn href=#ruby-annotation-box title=annotations>annotations</a>,
even in the case of <a class=css data-link-type=maybe href=#valdef-ruby-position.inter-character title=inter-character>inter-character</a> <a data-link-type=dfn href=#ruby-annotation-box title=annotations>annotations</a>.
<div class=figure>
<img alt='Diagram showing the line breaking opportunity in a "Bopomofo" ruby' src=images/r-break-b.gif>
<p class=caption><a class=css data-link-type=maybe href=#valdef-ruby-position.inter-character title=inter-character>inter-character</a> ruby line breaking opportunity
</div>
<h4 class="heading settled heading" data-level=2.8.1 id=break-between><span class=secno>2.8.1 </span><span class=content>
Breaking between bases</span><a class=self-link href=#break-between></a></h4>
<p>In typical cases, <a data-link-type=dfn href=#ruby-base-box title="ruby base boxes">ruby base boxes</a> and <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation boxes">ruby annotation boxes</a>
are styled to forbid internal line wrapping and do not contain forced breaks.
(See <a href=#default-stylesheet>Appendix A</a>.)
In such cases the <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a> can only break between adjacent <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>,
and only if no <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a> span those <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>.
<div class=figure>
<p><img alt="Diagram showing the line breaking opportunity in a complex ruby" src=images/r-break-a.gif>
<p class=caption>Ruby line breaking opportunity
</div>
<p>Whether ruby can break between two adjacent <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>
is controlled by normal line-breaking rules for the base text,
exactly as if the <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a> were adjacent inline boxes.
(The annotations are ignored when determining soft wrap opportunities for the <a data-link-type=dfn href=#base-level title="base level">base level</a>.)
<div class=example>
<p>For example, if two adjacent ruby bases are “蝴” and “蝶”,
the line may break between them,
because lines are normally allowed to break between two Han characters.
However, if <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-text-3/#propdef-word-break title=word-break>word-break</a> is <span class=css data-link-type=maybe title=keep-all>keep-all</span>, that line break is forbidden.
<pre><ruby>蝴<rt>hú</rt>蝶<rt>dié</rt></pre>
</div>
<p>Inter-base white space is significant for evaluating line break opportunities between <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a>.
As with white space between inlines, it collapses when the line breaks there.
Similarly, annotation white space is also trimmed at a line break.
<div class=example>
<p>For example, given the following markup:
<pre><ruby><rb>one</rb> <rb>two</rb> <rt>1</rt> <rt>2</rt></ruby></pre>
<p>Due to the space, the line may break between “one” and “two“.
If the line breaks there, that space—and the space between “1” and “2”—disappears,
in accordance with standard CSS white space processing rules. <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3text title=biblio-css3text>[CSS3TEXT]</a>
</div>
<h4 class="heading settled heading" data-level=2.8.2 id=break-within><span class=secno>2.8.2 </span><span class=content>
Breaking within bases</span><a class=self-link href=#break-within></a></h4>
<p>For longer base texts, it is sometimes appropriate to allow breaking within a base-annotation pair.
For example, if an English sentence is annotated with its Japanese translation,
allowing the text to wrap allows for reasonable line breaking behavior in the paragraph.
<p class=issue id=issue-14d7c6b1><a class=self-link href=#issue-14d7c6b1></a>
Insert scanned example so people don’t think this is just the ramblings of an insane spec-writer.
<p>Line-breaking within a <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> is only allowed if the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-text-3/#propdef-white-space title=white-space>white-space</a> property
of the <a data-link-type=dfn href=#ruby-base-box title="ruby base">ruby base</a> and all its parallel <a data-link-type=dfn href=#ruby-annotation-box title=annotations>annotations</a> allow it,
and there exists a <i data-link-type=dfn title="soft wrap opportunity">soft wrap opportunity</i> <em>within</em> (i.e. not at the start or end)
the content of each base/annotation box.
Since there is no structural correspondence between fragments of content
within <a data-link-type=dfn href=#ruby-base-box title="ruby bases">ruby bases</a> and <a data-link-type=dfn href=#ruby-annotation-box title=annotations>annotations</a>,
the UA may break at any set of opportunities;
but it is recommended that the UA attempt to proportionally balance
the amount of content inside each fragment.
<p>There are no line breaking opportunities within <a class=css data-link-type=maybe href=#valdef-ruby-position.inter-character title=inter-character>inter-character</a> <a data-link-type=dfn href=#ruby-annotation-box title=annotations>annotations</a>.
<p>Ruby alignment takes place within each fragment, after line-breaking.
<h3 class="heading settled heading" data-level=2.9 id=ruby-bidi><span class=secno>2.9 </span><span class=content>
Bidi Reordering</span><a class=self-link href=#ruby-bidi></a></h3>
<p class=issue id=issue-abee447f><a class=self-link href=#issue-abee447f></a>
Constraints:
Text within a ruby base must remain contiguous,
and bases belonging to a single annotation must remain contiguous.
Still figuring out exactly to enforce these limitations in a sensible manner.
</p>
<h3 class="heading settled heading" data-level=2.10 id=line-height><span class=secno>2.10 </span><span class=content>
Ruby box and line stacking</span><a class=self-link href=#line-height></a></h3>
<p>The <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-line-height title=line-height>line-height</a> property controls spacing between lines in CSS.
When inline content on line is shorter than the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-line-height title=line-height>line-height</a>,
half-leading is added on either side of the content,
as specified in <a href=http://www.w3.org/TR/CSS21/visudet.html#line-height>CSS2.1§10.8</a>. <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=biblio-css21>[CSS21]</a>
<p>In order to ensure consistent spacing of lines,
documents with ruby typically ensure that the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-line-height title=line-height>line-height</a> is large enough
to accommodate ruby between lines of text.
Therefore, ordinarily, <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation containers">ruby annotation containers</a> and <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation boxes">ruby annotation boxes</a>
do not contribute to the measured height of a line’s inline contents;
any alignment (see <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-vertical-align title=vertical-align>vertical-align</a>) and line-height calculations
are performed using only the <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>,
exactly as if it were a normal inline.
<p>However, if the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-line-height title=line-height>line-height</a> specified on the <a data-link-type=dfn href=#ruby-container title="ruby container">ruby container</a>
is less than the distance between
the top of the top <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>
and the bottom of the bottom <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation container">ruby annotation container</a>,
then additional leading is added
on the appropriate side of the <a data-link-type=dfn href=#ruby-base-container-box title="ruby base container">ruby base container</a>
such that if a block consisted of three lines
each containing ruby identical to this,
none of the <a data-link-type=dfn href=#ruby-container title="ruby containers">ruby containers</a> would overlap.
<p class=note>Note that this does not ensure that the <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a> remain within the line box.
It merely ensures that <em>if all lines had equal spacing</em>
and equivalent amounts and positioning of <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotations">ruby annotations</a>,
there would be enough room to avoid overlap.
<p>Authors should ensure appropriate <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-line-height title=line-height>line-height</a> and <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/box.html#propdef-padding title=padding>padding</a> to accommodate ruby,
and be particularly careful at the beginning or end of a block
and when a line contains inline-level content
(such as images, inline blocks, or elements shifted with <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-vertical-align title=vertical-align>vertical-align</a>)
taller than the paragraph’s default font size.
<div class=figure>
<p><img alt="The content of each line sits in the middle of its line height;
the additional space on each side is called half-leading.
Ruby fits between lines if it is smaller than twice the half-leading,
but this means that it occupies space belonging to the half-leading of the previous line." src=images/rlh-a.gif>
<p class=caption>Ruby annotations will often overflow the line;
authors should ensure content over/under a ruby-annotated line
is adequately spaced to leave room for the ruby.
</div>
<p class=note>More control over how ruby affects alignment and line layout
will be part of the CSS Line Layout Module Level 3.
Note, it is currently in the process of being rewritten;
the current drafts should not be relied upon.
<h2 class="heading settled heading" data-level=3 id=ruby-props><span class=secno>3 </span><span class=content>
Ruby Properties</span><a class=self-link href=#ruby-props></a></h2>
<p>The following properties are introduced to control ruby positioning and alignment.
<h3 class="heading settled heading" data-level=3.1 id=rubypos><span class=secno>3.1 </span><span class=content>
Ruby positioning: the <a class=property data-link-type=propdesc href=#propdef-ruby-position title=ruby-position>ruby-position</a> property</span><a class=self-link href=#rubypos></a></h3>
<table class=propdef>
<tr>
<th>Name:
<td><dfn class=css-code data-dfn-type=property data-export="" id=propdef-ruby-position>ruby-position<a class=self-link href=#propdef-ruby-position></a></dfn><tr>
<th><a href=#values>Value</a>:
<td>[ over | under | inter-character ] && [ right | left ]
<tr>
<th>Initial:
<td>over right
<tr>
<th>Applies to:
<td>ruby annotation containers
<tr>
<th>Inherited:
<td>yes
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per grammar</abbr>
</table>
<p>This property controls position of the ruby text with respect to its base.
Values have the following meanings:
<p class=issue id=issue-8b54b949><a class=self-link href=#issue-8b54b949></a><span class=issuehead>Issue-107: </span> Roland Steiner has requested the addition of an auto value as default. See <a href="http://www.w3.org/Search/Mail/Public/advanced_search?keywords=&hdr-1-name=subject&hdr-1-query=ruby-position%3A+undesirable+default+value+%27before%27+for+complex+ruby&hdr-2-name=from&hdr-2-query=&hdr-3-name=message-id&hdr-3-query=&period_month=&period_year=&index-grp=Public__FULL&index-type=t&type-index=www-style&resultsperpage=20&sortby=date">this thread</a> and <a href="http://www.w3.org/Search/Mail/Public/advanced_search?keywords=&hdr-1-name=subject&hdr-1-query=Styling+of+complex+Ruby&hdr-2-name=from&hdr-2-query=&hdr-3-name=message-id&hdr-3-query=&period_month=&period_year=&index-grp=Public__FULL&index-type=t&type-index=public-i18n-core&resultsperpage=20&sortby=date">this one</a>.</p>
<dl data-dfn-for=ruby-position>
<dt><dfn class=css-code data-dfn-for=ruby-position data-dfn-type=value data-export="" id=valdef-ruby-position.over><a class=css data-link-type=maybe href=#valdef-ruby-position.over title=over>over</a><a class=self-link href=#valdef-ruby-position.over></a></dfn>
<dd>The ruby text appears <a data-link-type=dfn href=http://dev.w3.org/csswg/css-writing-modes-3/#over title=over>over</a> the base in horizontal text.
<div class=figure>
<p><img alt="Diagram of ruby glyph layout in horizontal mode with ruby text appearing above the base" src=images/shinkansen-top.gif>
<p class=caption>Ruby over Japanese base text in horizontal layout
</div>
</dd>
<dt><dfn class=css-code data-dfn-for=ruby-position data-dfn-type=value data-export="" id=valdef-ruby-position.right><a class=css data-link-type=maybe href=#valdef-ruby-position.right title=right>right</a><a class=self-link href=#valdef-ruby-position.right></a></dfn>
<dd>The ruby text appears on the right side of the base in vertical text.
<div class=figure>
<p><img alt="Diagram of ruby glyph layout in vertical mode with ruby text appearing vertically on the right of the base" src=images/shinkansen-right.gif width=33>
<p class=caption>Ruby to the right of Japanese base text in vertical layout
</div>
</dd>
<dt><dfn class=css-code data-dfn-for=ruby-position data-dfn-type=value data-export="" id=valdef-ruby-position.under><a class=css data-link-type=maybe href=#valdef-ruby-position.under title=under>under</a><a class=self-link href=#valdef-ruby-position.under></a></dfn>
<dd>The ruby text appears under the base in horizontal text.
This is a relatively rare setting used in ideographic East Asian writing systems,
most easily found in educational text.
<div class=figure>
<p><img alt="Diagram of ruby glyph layout in horizontal mode with ruby text appearing below the base" src=images/shinkansen-bottom.gif>
<p class=caption>Ruby under Japanese base text in horizontal layout
</div>
</dd>
<dt><dfn class=css-code data-dfn-for=ruby-position data-dfn-type=value data-export="" id=valdef-ruby-position.left><a class=css data-link-type=maybe href=#valdef-ruby-position.left title=left>left</a><a class=self-link href=#valdef-ruby-position.left></a></dfn>
<dd>The ruby text appears on the left side of the base in vertical text.
<div class=figure>
<p><img alt="Diagram of ruby glyph layout in vertical mode with ruby text appearing vertically on the left of the base" src=images/shinkansen-left.gif>
<p class=caption>Ruby to the left of Japanese base text in vertical layout
</div>
</dd>
<dt><dfn class=css-code data-dfn-for=ruby-position data-dfn-type=value data-export="" id=valdef-ruby-position.inter-character><a class=css data-link-type=maybe href=#valdef-ruby-position.inter-character title=inter-character>inter-character</a><a class=self-link href=#valdef-ruby-position.inter-character></a></dfn></dt>
<dd>
<p>The ruby text appears on the right of the base in horizontal text.
This value forces the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-writing-modes-3/#propdef-writing-mode title=writing-mode>writing-mode</a> of the <a data-link-type=dfn href=#ruby-annotation-box title="ruby annotation">ruby annotation</a> to be vertical.
<p>This value is provided for the special case of traditional Chinese
as used especially in Taiwan:
ruby (made of <a href=#g-bopomofo>bopomofo</a> glyphs) in that context
appears vertically along the right side of the base glyph,
even when the layout of the base characters is horizontal:
<div class=figure>
<p><img alt="Example of Taiwanese-style ruby" src=images/bopomofo.gif>
<p class=caption>“Bopomofo” ruby in traditional Chinese
(ruby text shown in blue for clarity) in horizontal layout
</div>
<p class=note>
Note that the user agent is responsible for ensuring the correct relative alignment and positioning of the glyphs,
including those corresponding to the tone marks, when displaying.
Tone marks are spacing characters that occur (in memory) at the end of the ruby text for each base character.
They are usually displayed in a separate column to the right of the bopomofo characters,
and the height of the tone mark depends on the number of characters in the syllable.
One tone mark, however, is placed above the bopomofo, not to the right of it.
</dd>
</dl>
<p>If multiple <a data-link-type=dfn href=#ruby-annotation-container-box title="ruby annotation containers">ruby annotation containers</a> have the same <a class=property data-link-type=propdesc href=#propdef-ruby-position title=ruby-position>ruby-position</a>,
they stack along the block axis,
with lower levels of annotation closer to the base text.
<h3 class="heading settled heading" data-level=3.2 id=collapsed-ruby><span class=secno>3.2 </span><span class=content>
Collapsed Ruby Annotations: the <a class=property data-link-type=propdesc href=#propdef-ruby-merge title=ruby-merge>ruby-merge</a> property</span><a class=self-link href=#collapsed-ruby></a></h3>
<table class=propdef>
<tr>
<th>Name:
<td><dfn class=css-code data-dfn-type=property data-export="" id=propdef-ruby-merge>ruby-merge<a class=self-link href=#propdef-ruby-merge></a></dfn><tr>
<th><a href=#values>Value</a>:
<td>separate | collapse | auto
<tr>
<th>Initial:
<td>separate
<tr>
<th>Applies to:
<td>ruby annotation containers
<tr>
<th>Inherited:
<td>yes
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media: